Often it's desirable to have more than one camera on a robot, for example to provide front and back views.  As always, camera code should run in its own thread to prevent a camera exception (e.g. if a camera fails or gets unplugged) from taking down the main robot thread.  The example below shows how to create a new thread class called Cameras that creates two cameras and lets you switch between them using an Xbox controller.

WPILib provides a great helper class called [https://first.wpi.edu/FRC/roborio/release/docs/java/edu/wpi/first/cameraserver/CameraServer.html CameraServer] that does most of the heavy lifting.  You can read about it [https://docs.wpilib.org/en/latest/docs/software/vision-processing/introduction/cameraserver-class.html here] and [https://s3.amazonaws.com/screensteps_live/exported/Wpilib/2078/6264/Read_and_process_video_CameraServer_class.pdf?1483739157 here]

For more info about using multiple cameras, see [https://docs.wpilib.org/en/latest/docs/software/vision-processing/introduction/using-multiple-cameras.html here]

== Robot.java ==
{{{
#!java
package frc.robot;

import edu.wpi.first.wpilibj.TimedRobot;
import edu.wpi.first.wpilibj.XboxController;

public class Robot extends TimedRobot {
  Cameras cameras;
  XboxController xbox;

  @Override
  public void robotInit() {
    xbox = new XboxController(0); // create xbox controller object
    cameras = new Cameras();      // create the Cameras thread
    cameras.start();              // start thread and launch its run() method
  }

  @Override
  public void robotPeriodic() {
    if (xbox.getAButton()) {
      cameras.selectFront();
    } else if (xbox.getBButton()) {
      cameras.selectRear();
    }
  }
}
}}}

== Cameras.java ==
Create a new file named Cameras.java under src/main/java/frc/robot (same folder as Robot.java):
{{{
#!java
package frc.robot;

import edu.wpi.first.cameraserver.CameraServer;
import edu.wpi.cscore.UsbCamera;
import edu.wpi.cscore.VideoSource.ConnectionStrategy;


class Cameras extends Thread {
    CameraServer   camServer;
    UsbCamera      frontCam, rearCam;

    public Cameras() {
        // Camera server manages all cameras and streams
        camServer = CameraServer.getInstance();
        // Start serving front camera (USB port 0)
        frontCam = camServer.startAutomaticCapture("cameras", 0);
        // Create additional camera(s)
        rearCam   = new UsbCamera("rear", 1);

        // keep video streams open for fast switching
        //frontCam.setConnectionStrategy(ConnectionStrategy.kKeepOpen);
        //rearCam.setConnectionStrategy(ConnectionStrategy.kKeepOpen);
    }

    public void selectFront() {
        camServer.getServer().setSource(frontCam);
    }
    
    public void selectRear() {
        camServer.getServer().setSource(rearCam);
    }

    // Run method is invoked when start method is called
    public void run() {
        while (true) {
            // run forever
        }
    }
}
}}}